1. Technical Field of the Invention
This invention relates to a process for preparing fluid cracking catalysts (FCC). Particularly, this invention relates to a process for preparing sol-based fluid cracking catalysts by adding acid or alkaline stable surfactants to the component streams prior to the spray drying.
2. Description of the Background Art
Catalyst manufacturers are continuously seeking methods to lower the cost of producing catalysts. Catalyst producers, typically, search for processes to lower the cost of raw materials or utilities, to build higher efficiency equipment or equipment with higher through-put and lower maintenance, or to provide better utilization of zeolite, binder, clay, or added alumina. All of these factors contribute to the direct manufacturing costs of catalysts.
The cost of energy, such as natural gas, has caused the industry to focus its attention on processes which raise the solids levels in feed slurry to a spray dryer. "Higher feed solids" in processes lower the expense of natural gas for spray drying procedures. A catalyst manufacturing facility producing 25,000 to 60,000 tons per year can achieve a savings of a few hundred thousand dollars to over a million dollars per year for every two percent increase in solids.
Numerous processes have been developed by the catalyst manufacturing industry to raise solids in-sol binder cracking catalyst production. One general approach that has not been successful is to add concentrated sodium silicate directly to a slurry of clay having about 70 percent solids wherein a portion of the dilution water, that is required for producing the required concentration of sodium silicate of about 12.5 to 13.3 percent SiO.sub.2, is supplied by the clay slurry water. A small, but not an insignificant quantity of process water is still necessary with the slurry water method to achieve the proper silicate concentration.
The "CSS process" for producing fluid cracking catalysts involves a continuous mode of preparation of a clay-silicate-slurry using concentrated sodium silicate, high solids kaolin slurry, and process water to achieve the proper concentration of silicate expressed as the percent of SiO.sub.2. The resulting clay-silicate-slurry is continuously metered against a stream of acidified alum such as 12.5 percent H.sub.2 SO.sub.4 and 3.0 percent Al.sub.2 O.sub.3. Typically, both streams are fed simultaneously into a suctionside of a centrifugal pump or high shear low volume mixer to produce a usable binder. The discharge from the mixing device is then metered continuously against metered streams of zeolite and, in some instances, a stream of alumina depending on the functionality desired for the finished catalyst.
The industry's attempts to produce catalysts by CSS processes have generally resulted in a catalyst material with poor attrition resistance and low bulk density. These two undesirable attributes result in production cost savings, but provide catalysts that are commercially non-competitive.
U.S. Pat. Nos. 3,140,249; 3,140,253; 3,210,267; 3,271,418; 3,436,357; and 3,459,680 to Plank and Rosinski disclose molecular sieve-type cracking catalysts. The world-wide petroleum refining industry rapidly adopted the use of these catalysts in the early 1960's because these catalysts provided significant increases in gasoline yields and improved the coke selectivity obtained with zeolite-containing catalysts when compared to catalysts that are based upon amorphous silica-alumina.
The first molecular sieve-type cracking catalysts incorporated rare earth-stabilized faujasite with silica-alumina in ratios between 2.5 and 3.0. These early formulations were simple admixtures of zeolite-molecular sieves with the amorphous silica-alumina and clay-synthetic gel materials that were previously used alone as cracking catalysts. The molecular sieve component of these catalysts was, typically, added prior to spray drying to the gel slurry. The rapid initial success of these catalysts, because of their increased yield and operational benefits, resulted in the petroleum refining industry demanding fluid cracking catalysts that contained molecular sieves with high silica-alumina ratios. These catalysts provided molecular sieves with silica-alumina ratios approach a value of 5. This ratio imparts superior thermal and hydrothermal stability to a catalyst. The demand was further stimulated by the high temperature regeneration technology introduced in the mid-seventies such as that disclosed in U.S. Pat. No. 3,844,973, and the almost simultaneous development of combustion promoter additives for regeneration of fluid cracking catalysts such as those described in U.S. Pat. No. 4,072,600.
Acceptance of these technologies by the refining industry demanded catalyses with molecular sieves of a higher silica-alumina or "faujasite-type" ratio with higher maintenance of cracking activity or "stability." This demand was due to the more severe operating conditions to which the catalyst was subjected.
Current processes for removing lead from gasoline has further sustained the world-wide demand for high silica-alumina ratio sieves. This demand is due to the improvement in gasoline octane which can be obtained catalytically by converting high silica-alumina ratio molecular sieves into a modified form known as ultrastable-Y or USY materials. The ultrastable form of Y-zeolite can be achieved by conversion of the sodium form of Y-zeolite (faujasite) before its incorporation into a catalyst. The entire catalyst particle can, alternatively, be treated under conditions which result in an in situ conversion of faujasite within the microsphere itself. The higher the silica-alumina ratio of the starting NaY zeolite, the higher the quality and performance of the resulting ultrastable-Y materials that are prepared either ex-situ or in situ. The phenomenon is, also, noted in the molecular sieves sold under the trade name LZ 210 by Union Carbide Corporation.
There are a number of patents describing processes for preparing molecular sieve-type catalysts including U.S. Pat. No. 3,425,956. U.S. Pat. No. 3,867,308 discloses the use of a silica-sol type binding system in the preparation of zeolite promoted catalysts. U.S. Pat. No. 3,957,689 discloses alum buffered silica-sol. These catalysts, that are based on "sol technology" for the binding system, were developed in response to an increased demand for harder and higher density catalysts to meet the ever tightening environmental constraints being placed on the petroleum refining industry. These patents are typical of the large body of art in this area.
The introduction of sol bound catalysts provided catalysts having significant improvements in density and hardness. However, examination of these catalyst by Scanning Electron Microscopy (SEM) revealed that almost every microspheriodal fluid cracking catalyst particle possessed a "blow-hole" or a cavernous region which caused the particle to be more likely to break into two or more smaller fragments during the FCC operation. When catalyst particles break during the FCC operation, the smaller particle fragments are almost instantly lost through a regenerator flue gas stack. If the particle breakage occurs on the reactor side of the equipment, the slurry oil stream becomes over-loaded with catalyst dust referred to as "fines." This condition can result in the total suspension of the operation of the FCC unit. Such a shutdown of FCC operation is extremely costly to a refinery due to both lost product and unscheduled maintenance expenses. The occurrence of "blow-holes" in catalyst particles can be reduced by changes in the catalyst manufacturing process. These process changes are not necessarily easy or economical and do not eliminated the occurrence of "blow-holes."
The industry lacks efficient and economical methods to produce catalysts having microspheroidal particles without a significant presence of "blow-holes" or cavernous openings.